This invention pertains to a vane-type double lobe pump for hydraulic fluid having a variable volume capability derived from different contouring by different radii of curvature of the lobes or sections of a cam ring which control the pumping displacements of the vanes of the pump and with the pumping displacement being derived from pumped volume between vanes, as well as pumped volume from rotor slots beneath the vanes.
A variable volume vane-type pump normally has a cam ring controlling the pumping displacement of the vanes which is movable to various positions with respect to a rotor carrying the vanes, to provide variable volume. Such pumps have required the use of structure for appropriately sealing and movably mounting as well as locating the cam ring dependent upon the desired volume output of the pump.
Applicants have a prior application, Ser. No. 470,988, filed May 17, 1974, now U.S. Pat. No. 3,953,153, which is owned by the assignee of this application, wherein several embodiments of a multiple displacement pump system and method are disclosed. In said prior application, a vane-type pump with a fixed cam ring has pumping action derived by pumping from spaces between vanes as well as from the rotor slots beneath the vanes. The pump is of the double lobe type and with the cam ring having two elliptical sections of the same contour. The variable volume capability is obtained by utilizing the total flow from both the intervane and undervane pumping spaces or using only one or the other, with the volume that is not to be utilized being returned to the inlet means for the pump. In these structures, the variation in volume is obtained by selectively between use of either the undervane slots or the intervane spaces. When pumping volume is obtained from the undervane spaces, only, there is leakage to the intervane spaces past the vanes from the rotor slots which reduces pump efficiency. Additionally, there is no disclosure in the structures of said prior application for providing four different volume rates for the pump.
The Adams et al U.S. Pat. No. 2,832,199 discloses a single lobe vane-type pump wherein plural volumes are taken from the pump by having plural outlet ports arcuately spaced along the arc of travel of the vanes whereby an outlet line connected to each of the outlet ports receives a selected amount of the pumped volume. This patent does not show a double lobe vane-type pump with plural volume outputs from intervane and undervane spaces, nor selective volume control.